This invention relates to door lock assemblies designed to withstand the application of excessive torque. More particularly, the invention relates to door lock assemblies including a latching system specially coupled to a door handle such as a lever handle or the like so that the door handle disconnects from the latching system under application of excessive torque, thereby preserving the integrity of the latching system.
The invention is of particular utility for door lock assemblies having lever handles, since lever handles are particularly susceptible to the manual application of excessive torque--for example, through use of a pry bar or other tool, or even through the direct wrenching force from the hand of a strong person. Such lever handles are used with increasing frequency today--indeed, may be mandatory in certain settings--because they can easily be operated by handicapped persons or others unable to grip and turn a more conventional knob.
The prior art recognizes the need for a torque-release feature in door lock assemblies. For example, Foshee U.S. Pat. No. 4,773,240 relates to a torque-releasable latching system comprising a body assembly yieldably interconnected to a handle shell via a drive assembly. The drive assembly includes a pair of mateable female and male drive rings. Under application of excessive torque, the male drive ring reciprocates to an inactive position, out of torque-transmitting engagement with the female drive ring. Yang U.S. Pat. No. 4,679,420 also describes a force immune door latch. The door latch in Yang is provided with a resiliently-biased ratcheting means having a biasing force oriented in a direction perpendicular to the longitudinal axis of the door latch shaft. Best, et al U.S. Pat. No. 4,550,581 provides another example. There, application of excessive torque causes the shearing of drive lugs in a frangible drive, thus disengaging the lock assembly from the handle shell. Of course, such a frangible drive is not resettable once the shearing has occurred.
It is thus an object of the present invention to provide a torque-releasable assembly that is resettable after the application of excessive door lock torque has caused disengagement of the handle shell.
A further object of this invention is to provide a torque-releasable door lock assembly with a simple release mechanism that is constructed and assembled easily.
Another object of this invention is to provide a torque-releasable assembly that will maintain a normal driving connection door lock between the handle shell and the body assembly under an applied torque of up to approximately 250-300 in-lb's as applied to the handle shell, but will disengage the body assembly from the handle shell for torques greater than about 300 in-lb's applied to the handle shell.
According to the present invention, a torque-releasable door handle assembly is provided for operating a door latching system. The door handle assembly includes a handle shell preferably including a radially-extending front face and a radially-extending back face situated to lie in spaced apart relation to the front face. Extending between the front and back faces is an axially-extending side wall. The front face, side wall, and back face cooperate to define a hollow interior cavity within the handle shell.
The door handle assembly also preferably includes a rotatable body having a forward portion and a rearward portion. The forward portion extends into the hollow interior cavity of the handle shell to define a detent chamber therein. Importantly, the forward portion has an exterior surface facing the handle shell and is formed to include a radially outwardly opening groove. The rearward portion lies outside of the hollow interior cavity and is mountable in the door to permit rotation of the body with respect to the door.
Drive means is provided for yieldably interconnecting the forward portion of the body and the handle shell to establish a normal driving connection between the forward portion of the body and the handle shell, such connection enabling the forward portion of the body to be rotated about an axis of rotation in response to a torque applied to the handle shell. The drive means is configured to engage the groove to establish the normal driving connection. The drive means is also designed to disengage the groove in response to the application of at least a predetermined amount of torque to the handle shell. Such a disengagement from the groove breaks the normal driving connection. Thus, this feature of the invention serves to minimize the possibility that the integrity of the door latching system will be breached.
In a preferred embodiment, the handle shell includes a lever handle. The drive means is positioned on the opposite side of the axis of rotation from the lever handle. The drive means includes a detent bar and at least one Bellville washer for yieldably biasing the detent bar into the groove. A support block slidably received in the handle shell is provided to support the at least one Bellville washer. The detent bar is slidably received in a channel formed on the support block. Advantageously, retainer means is provided for retaining both the drive means and the forward portion of the body within the handle shell. Thus, the drive means and the forward portion of the body are located forward of the retainer means with respect to the handle shell, providing easy assembly.
The various features and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of a preferred embodiment exemplifying the best mode of carrying out the invention as presently perceived.